As an image output device, there may be, for example, known image display device, such as a display including a liquid crystal panel, an organic electroluminescence panel, or any other type of display panel, and image printing device, such as an inkjet printer, a laser printer, and an LED printer. An image output device of this type may output an image in accordance with an externally transmitted signal carrying chromaticity specified based on the NTSC method, the sRGB method, the CMYK method, or any other standard or method but actually output the image by using chromaticity according to the characteristics specific to the image output device. The image output device may therefore actually display an image by using chromaticity different from the chromaticity carried by the externally transmitted signal. To regenerate the original chromaticity carried by the externally transmitted signal, there may be a known technology called linear matrix conversion, in accordance with which the signal is corrected.
For example, Japanese Patent Publication No. 2011-223467 discloses a color signal processing device that may perform linear matrix conversion in which an RGB signal is multiplied by a 3×3 matrix coefficient. The color signal processing device may include an approximate coefficient storage section that stores approximate coefficients of each approximate equation, a matrix coefficient calculation section that substitutes the value of a first color in an inputted RGB signal into an approximate equation expressed by the approximate coefficients read from the approximate coefficient storage section to calculate a 3×3 matrix coefficient according to the inputted RGB signal, and a conversion section that multiplies the inputted RGB signal by the matrix coefficient calculated by the matrix coefficient calculation section and outputs the color-converted RGB signal. The approximate equation may determine an approximate value of the matrix coefficient and have a variable that is the value of the first color of the three primary colors R, G, and B.
Further, for example, Japanese Patent Publication No. 2006-013968 discloses a color conversion device that may perform color conversion on an inputted color signal formed of five or more color components. The color conversion device may include coefficient storage means for storing a matrix conversion coefficient and operation means for reading the matrix conversion coefficient stored in the coefficient storage means to perform matrix operation and performing color conversion on the inputted color signal. The operation means may perform the matrix operation in consideration of a correlated element relating to color components that interact with each other among the color components described above.
To regenerate the original chromaticity carried by an externally transmitted signal, there may be a known technology for correcting the signal more precisely by using a three-dimensional lookup table.
For example, Japanese Patent Publication No. H4-21191 discloses a color conversion device using a three-dimensional lookup table. The color conversion device may include division means for receiving a set of three-dimensional color signals, four-dimensional color signals, or color signals having a dimension of a higher degree and dividing each of the color signals into an upper-level signal and a lower-level signal with the numbers of bits of the two signals different from each other, a table memory for storing color conversion values selected by the upper-level signals, weight coefficient provision means for providing values of weight coefficient selected by the lower-level signals, unit tetrahedron selection means for selecting a unit tetrahedron to which the color signal belongs from a plurality of unit tetrahedrons obtained by dividing a unit cuboid in a color space determined by the upper-level signals, and operation means for performing three-dimensional interpolation, four-dimensional interpolation, or interpolation of a dimension of a higher degree on the color space based on color conversion values and the weight coefficient values at four vertices of the unit tetrahedron.